The generation of 02- by phagocytic cells requires the assembly of a membrane-bound complex known as the NADPH oxidase, which is composed of an integral plasma membrane flavocytochrome b and four cytosolic proteins (p40 phox, p47 phox, p67 phox, and Rac2). Although progress has been made, there is limited information about how each of these proteins regulate formation of the active NADPH oxidase complex and, similarly, what turns off the system. In the previous grant period, we identified a number of protein-protein interactions among the NADPH oxidase protein components and investigated how these interactions related to assembly of the active 02- generating system. In this renewal application, we propose studies to investigate how NADPH oxidase assembly is regulated. Based on studies performed under the previous grant period, studies by others on the phagocyte NADPH oxidase, and preliminary work described here, we hypothesize that neutrophil capacity for oxidase assembly and oxidase assembly per se are regulated at several different levels, including transcription and biosynthesis of the phox proteins, molecular assembly of the active system, and lateral organization in plasma membrane domains. Consequently, appropriate NADPH oxidase activity results from integration of these multiple levels of regulation. Because of the complex nature of the oxidase, we propose to address this hypothesis by focusing this project primarily on the role of the cytosolic phox factors in oxidase regulation. Specifically, this proposal describes strategies for: 1) characterizing the promoter for p67 phox and determining what transcription factors regulate p67 phox transcription; 2) characterizing cytosolic phox protein gene expression; 3) analyzing biosynthesis of the cytosolic phox proteins to determine relative stability of these proteins and kinetics of protein turnover; 4) identifying and characterizing flavocytochrome b domains that bind p67 phox and Rac; and 5) develop cell lines expressing GFP-phox fusion proteins for use analysis of the intermolecular interactions between cytosolic oxidase proteins and the oxidase complex in vivo. The results of these studies will further our understanding of how distinct levels of regulatory input are integrated to facilitate functional assembly and activation of the phagocyte NADPH oxidase.